如何使用for-loop构建Spring Data Mongo聚合操作

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-mongodb</artifactId>
</dependency>

@Document(collection = "users")
public class User {
    @Id
    private String id;
    private String name;
    private int age;
    // 其他字段和对应的getter和setter方法
}

@Autowired
private MongoTemplate mongoTemplate;

public double calculateAverageAge() {
    Aggregation aggregation = Aggregation.newAggregation(
        Aggregation.group().avg("age").as("averageAge")
    );

    AggregationResults<AverageAgeResult> results = mongoTemplate.aggregate(
        aggregation, "users", AverageAgeResult.class
    );

    AverageAgeResult result = results.getUniqueMappedResult();
    return result.getAverageAge();
}

private static class AverageAgeResult {
    private double averageAge;
    // getter和setter方法
}

double averageAge = calculateAverageAge();
System.out.println("Average age: " + averageAge);